This invention relates to a method of treating a permeable structure such as a permeable subterranean formation using water-soluble organic polycationic polymers containing three quaternary ammonium moieties in the monomer repeat units in order to stabilize in the structure migrating fines such as silicate, iron minerals, and alkaline earth metal carbonates or swelling clays or combinations thereof.
The recovery of fluids such as oil or gas has been troublesome in areas where a subterranean formation is composed of one or more layers or zones which contain swelling clays such as clays in the smectic group including clay materials such as montmorillonite, beidellite, nontromite, saponite, hectorite, and sauconite or migrating fines such as silica, iron minerals and alkaline earth metal carbonates. At times during the recovery of formation fluids from the particular layers or zones of the formation, the clays swell or the fines migrate to the wellbore and block the passageways leading to the wellbore. This swelling or migration is often a particular problem when swelling clays or migrating fines are contacted with water foreign to the formation. Plugging or materially impairing the flow of the formation fluids towards the wellbore results in a loss of these fluids to the producer or so decreases the rate of hydrocarbon recovery from the well as to cause the well to be shut down because it is economically unattractive to produce therefrom. An additional adverse factor resulting from the movement of fines towards the wellbore is that the fines are often carried along with the formation fluids to the wellbore and pass through pipes, pumps, etc., being used to recover the formation fluids to the surface with resulting damage to the moving parts as the fines are very abrasive.
Secondary and tertiary methods of recovering hydrocarbons from a subterranean formation are well known. In general, such a method involves introducing a fluid, such as water, steam, etc., into one or more injection wells which penetrate the formation and forcing the fluid toward one or more of said producing wells. Swelling clays or migrating fines or combinations thereof during such an operation can cause a decrease in the rate in which fluid can be injected into the formation and can decrease the permeability or porosity of the formation which results in a decrease in the rate of hydrocarbon production at the offset production wells.
Swelling clays or migrating fines or combinations thereof are frequently encountered during acidizing or fracturing operations and during sand consolidation operations. The presence of the clays or migrating fines or combinations thereof during these operations can result in a decrease in the permeability of the formation which is being treated.
Gravel packing is a widely practiced method of preventing the production of sand from poorly consolidated formations. The swelling of the clays or the migration of fines or combinations thereof into the gravel pack can greatly reduce the permeability of the gravel pack. This can result in a decrease in the rate of production of hydrocarbons from the formation.
Numerous attempts have been made heretofore to control the ill effects of water on swelling clays or migrating fines or combinations thereof in subterranean formations. For example, treating solutions containing cations such as potassium, calcium, ammonium, and hydrogen ions have been introduced into clay-containing subterranean formations whereby the clays are contacted thereby. Ions contained in the clays are replaced by ions in the solutions thereby transforming the clays into relatively non-swelling forms. While success has been achieved with this method, the exchanging of the other ions for ions in the clays is only a temporary remedy in that counter-replacement can readily take place.
In order to make the replacement of ions in the clays more permanent, inorganic polycationic polymers or complexes have been utilized in lieu of simple cations. Such inorganic polycationic polymers or complexes have been successful in controlling swelling clays but have their various limitations. For example, the most commonly used inorganic polycationic polymers are zirconyl chloride (ZrOCl.sub.2) and aluminum hydroxy chloride (Al(OH).sub.x Cl.sub.y). Aluminum hydroxy chloride requires a cure time after it is placed in the presence of the clay which is disadvantageous in that rig and production times are consumed during the wait. Also, aluminum hydroxy chloride can tolerate only a limited amount of carbonate material in the formation and is removed by contact with acids such as when a subsequent acid treatment of the formation is necessary. Zirconyl chloride is limited in the pH range of the placement fluid and can be removed by acid under certain conditions.
Organic polycationic polymers have also been utilized for stabilizing clays or migrating fines or combinations thereof. For instance, U.S. Pat. Nos. 4,366,071; 4,366,072; 4,366,073; 4,366,074; 4,374,739; 4,360,483; 4,460,483; and 4,462,718 disclose the use of organic polycationic polymers to prevent or reduce the ill effects of swelling clays or migrating fines or combinations thereof in subterranean formations. These patents are assigned to the assignee of the present invention and are hereby incorporated by reference.
U.S. Pat. Application Ser. No. 478,573 filed Mar. 24, 1983, now U.S. Pat. No. 4,497,596, by John K. Borchardt and Bill M. Young discloses and claims a method of treating a permeable subterranean formation using water-soluble organic polycationic polymers containing two quaternary ammonium moieties in the polymer repeat units in order to stabilize in the formation migrating fines in presence or absence of swelling clays. This patent application is assigned to the assignee of the present invention and is hereby incorporated by reference.
The present invention is a method of preventing or reducing the migration of fines or the swelling of clays or combinations thereof within a permeable structure such as a subterranean formation by contacting the swelling clays or migrating fines or combinations thereof in the permeable structure with an effective amount of organic polycationic polymers containing three quaternary ammonium moieties in the monomer repeat units.
The organic polycationic polymers used in the method of the invention are very effective in treating swelling clays such as clays in the smectic group including clay minerals such as montmorillonite, beidellite, nontromite, saponite, hectorite and sauconite and fines such as silica, iron minerals such as hematite, magnetite, lepidocrocite, wuestite, akaganeite and siderite, and alkaline earth metal carbonates such as calcite and dolomite. The organic polycationic polymers are particularly effective when used in conjunction with acidizing operations that utilize strong mineral acids such as 15% by weight hydrochloric acid or mixtures of 3% by weight hydrofluoric acid and 12% by weight hydrochloric acid. Furthermore, the organic cationic polymers are very effective over a wide range of temperatures and particularly effective from about 90.degree. F. to about 200.degree. F. A treatment with the organic polycationic polymers of the present invention is essentially permanent and the polymers are very resistant to being removed by brines, oils and acids. Permeable structures, such as subterranean formations, exhibit high permeability retention after the structure has been treated with the organic polycationic polymers. No well shut-in time is required when the organic polycationic polymers are used to carry out the method of the invention.